The problem of electrically insulating a spray gun, under high voltage, of an electrostatic paint shop from the remaining paint shop parts has already been discussed in DE 102 33 006 A1. It is proposed there in connection with a scrapeable paint supply system to in each case move scrapers (“go-devils”) by means of blowing air so that a line section of predetermined length of the conveying lines made of electrically insulating plastics material is in each case filled with air and is thus paint-free.
In order to ensure that the in each case desired electrical insulation between the high voltage part and the part of the unit at earth potential is guaranteed, the position of various scrapers must be monitored by using detectors, in which a distinction always has to be made between scrapers that form the boundary of the front end of a paint packet and scrapers that form the boundary of the rear end of a paint packet. Similar problems arise when conveying electrically conducting solvents in lines of electrostatic paint shops and also in conjunction with other consumers to be connected to a high voltage, for example electrostatic spray cones or similar electrostatic spraying devices.
There is also the problem of the mutual electrical separation of sections of a conveying line not only in the case of liquid media but also with gaseous and flowable pulverulent media. In the following description and in the claims these media are jointly understood to be fluids.
In this known procedure the line section freed from liquid is filled with air under a slight excess pressure that is just sufficient to move the scrapers.